I just read the full announcement and changelog. This was important enough that I thought I would include it here ...

What about jQuery UI 1.7?

The release of jQuery UI 1.8 final makes it the latest stable release of jQuery UI. This makes the previous release, 1.7.2, legacy. The jQuery UI project supports the latest stable and a single legacy release concurrently. So as of now, the jQuery UI Download Builder and ThemeRoller only contain these releases. Any release older than 1.7.2 is no longer supported and all users are encouraged to upgrade to 1.8 as soon as possible.

A few issues have been identified in attempting to use legacy jQuery UI 1.7.2 with the latest jQuery 1.4.2. These versions are not compatible. The legacy jQuery UI 1.7.2 is only compatible with jQuery 1.3.2. The coming jQuery UI 1.7.3 release will bring it up to compatibility with the latest jQuery 1.4.2. This will be the final 1.7.x release, freezing this branch.